Field of the Invention
The object of the present invention is a method and an apparatus for controlling tyres.
Description of the Related Art
The tyre production cycles provide for obtaining and/or assembling the various components of a tyre being processed in one or more building lines, and subsequently subjecting the green tyre to a moulding and vulcanisation process adapted to define the structure of the tyre according to a desired geometry and tread pattern.
The tyre, when moulded and vulcanised, is defined by a toroidal structure wound around a rotation axis and substantially symmetric with respect to an axial middle line plane perpendicular to said rotation axis. In particular the toroidal structure comprises a crown portion arranged substantially perpendicular to the axial middle line plane in a radially external zone of the tyre, two anchorage portions arranged in radially internal zones of the tyre, respectively on opposite sides of the axial middle line plane, and two lateral portions that are respectively extended on opposite sides of the axial middle line plane between one of the anchorage portions and the crown portion.
With “axial middle line plane” it is intended a plane perpendicular to the rotation axis equidistant from the axially external portions of the tyre itself. With “crown portion” of the tyre it is intended a portion of the tyre arranged substantially perpendicular to the axial middle line plane, in a radially external zone of the tyre, and corresponding to the tread band and to portions of the belt structure and carcass arranged radially internal with respect to the tread band.
With “anchorage portions” of the tyre, also commonly defined “beads”, the radially internal zones of the tyre are intended, respectively arranged on opposite sides of the axial middle line plane, configured in a manner so as to be engaged with the rim of a wheel.
With “lateral portions” of the tyre, portions of the tyre are intended that are respectively extended on axially opposite sides of the axial middle line plane between each of the anchorage portions and the crown portion, corresponding to the sidewalls and to portions of the carcass arranged in axially internal position with respect to the aforesaid sidewalls.
With “abutted lateral portion” and with “free lateral portion” of the tyre it is respectively intended a lateral portion abutted against a support plane and the opposite lateral portion arranged at a specific height from the support plane.
With “measurement surface” it is intended a surface subjected to timely control having limited size with respect to the overall surface of said lateral portions.
With “measurement surfaces arranged in symmetric positions with respect to the axial middle line plane”, two measurement surfaces are indicated, each belonging to a lateral portion of the tyre and arranged at the same angular and radial position with respect to the rotation axis thereof.
US2006/0272408 describes a method and an apparatus for measuring the uniformity of the tyre. The method comprises the steps of mounting the tyre on a spindle, pressing a circumferential surface of a rotating drum against the tread surface of the tyre with a first pressing force, rotating the tyre around its axis, and calculating the forces on a first and a second plane of the tyre through calculation means while the tyre is rotating.
JP2008190981 describes a method and a device for measuring the rigidity of the sidewall of a tyre. A flattening force is applied by a pressure roller to a sidewall of a tyre on one side, in order to deform it. The movement on one side of said sidewall of the tyre is measured by measurement means and the rigidity of the sidewall is determined based on these detection and measurement results.
In the known production cycles, for identifying defects, the moulded and vulcanised tyre is subjected to a manual visual control or it can be subjected to an automatic control as is described in the abovementioned document.
One of such manual visual controls is directed towards discarding tyres in which the lateral portion has poor rigidity, i.e. for identifying the so-called “weak sidewall” defect, by sidewall it being intended a lateral portion of the finished tyre.